MAX1645-MAX1645A Maxim, MAX1645-MAX1645A Datasheet - Page 29

• Manufacturer Part Number: MAX1645-MAX1645A
• Description: Advanced Chemistry-Independent / Level 2 Battery Chargers with Input Current Limiting
• Manufacturer: Maxim

(Table 8). Level 3 smart battery chargers are supersets
of Level 2 chargers and, as such, support all Level 2
charger commands.
The Level 2 or smart battery-controlled smart battery
charger interprets the smart battery’s critical warning
messages and operates as an SMBus slave device to
respond to the smart battery’s ChargingVoltage() and
ChargingCurrent() messages. The charger is obliged to
adjust its output characteristics in direct response to
the ChargingVoltage() and ChargingCurrent() mes-
sages it receives from the battery. In Level 2 charging,
the smart battery is completely responsible for initiating
the communication and providing the charging algo-
rithm to the charger.
The smart battery is in the best position to tell the smart
battery charger how it needs to be charged. The charg-
ing algorithm in the battery may request a static charge
condition or may choose to periodically adjust the
smart battery charger’s output to meet its present
needs. A Level 2 smart battery charger is truly chem-
istry independent and, since it is defined as an SMBus
slave device only, the smart battery charger is relatively
inexpensive and easy to implement.
Table 10 lists the recommended components and
refers to the circuit of Figure 1; Table 9 lists the suppli-
Table 9. Component Suppliers
Inductor
MOSFET
Sense Resistor
Capacitor
Diode
COMPONENT
Battery Chargers with Input Current Limiting
Advanced Chemistry-Independent, Level 2
Selecting External Components
Level 2 Smart Battery Charger
Sumida
Coilcraft
Coiltronics
Internal Rectifier
Fairchild
Vishay-Siliconix
Dale
IRC
AVX
Sprague
Motorola
Nihon
Central
Semiconductor
MANUFACTURER
______________________________________________________________________________________
CDRH127 series
D03316P series
UP2 series
IRF7309
FDS series
Si4435/6
WSL series
LR2010-01 series
TPS series,
TAJ series
595D series
1N5817–1N5822
NSQ03A04
CMSH series
PART
ers’ contacts. The following sections describe how to
select these components.
Schottky diode D1 provides power to the load when the
AC adapter is inserted. Choose a 3A Schottky diode or
higher. This diode may not be necessary if P1 is used.
The P-channel MOSFET P1 turns on when V
V
sumption of the Schottky diode. To minimize power loss,
select a MOSFET with an R
MOSFET must be able to deliver the maximum current
as set by R1. D1 and P1 provide protection from
reversed voltage at the adapter input.
The N-channel MOSFETs N1 and N2 are the switching
devices for the buck controller. High-side switch N1
should have a current rating of at least 6A and have an
R
by BST; its current should be less than 10mA. Select a
MOSFET with a low total gate charge and determine
the required drive current by I
is the DC-DC converter maximum switching frequency
of 400kHz).
The low-side switch N2 should also have a current rat-
ing of at least 3A, have an R
and a total gate charge less than 10nC. N2 is used to
provide the starting charge to the BST capacitor C14.
During normal operation, the current is carried by
Schottky diode D2. Choose a 3A or higher Schottky
diode.
D3 is a signal-level diode, such as the 1N4148. This
diode provides the supply current to the high-side
MOSFET driver.
The P-channel MOSFET P2 delivers the current to the
load when the AC adapter is removed. Select a MOS-
FET with an R
loss and voltage drop.
Inductor L1 provides power to the battery while it is
being charged. It must have a saturation current of at
least 3A plus
The controller determines the constant off-time period,
which is dependent on BATT voltage. This makes the
ripple current independent of input and battery voltage
and should be kept to less than 1A. Calculate the ∆I
with the following equation:
Higher inductor values decrease the ripple current.
Smaller inductor values require higher saturation cur-
BATT
DS(ON)
. This eliminates the voltage drop and power con-
of 50mΩ or less. The driver for N1 is powered
1
DS(ON)
/
2
MOSFETs and Schottky Diodes
of the current ripple (∆I
I
SAT
∆I
of 50mΩ or less to minimize power
L
= 3A +
= 21Vµs / L
DS(ON)
DS(ON)
GATE
1
Inductor Selection
/
2
∆I
of 50mΩ or less. This
= Q
L
of 100mΩ or less,
GATE
L
).
· f (where f
CVS
29
>
L